linux-kernel - Re: [PATCH v5 08/12] x86/smpboot.c: Wake up CPU0 via NMI instead of INITs

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Message-ID: <CAMzpN2gFB0LuWqVA2KA13C3+g8Zb2irmFnpjwHOtOvhuE67KWQ@mail.gmail.com>
Date:	Thu, 12 Jan 2012 07:31:40 -0500
From:	Brian Gerst <brgerst@...il.com>
To:	Fenghua Yu <fenghua.yu@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	H Peter Anvin <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Asit K Mallick <asit.k.mallick@...el.com>,
	Tony Luck <tony.luck@...el.com>,
	Arjan van de Ven <arjan.van.de.ven@...el.com>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Len Brown <len.brown@...el.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Chen Gong <gong.chen@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-pm <linux-pm@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v5 08/12] x86/smpboot.c: Wake up CPU0 via NMI instead of INITs

On Wed, Jan 11, 2012 at 12:04 PM, Fenghua Yu <fenghua.yu@...el.com> wrote:
> From: Fenghua Yu <fenghua.yu@...el.com>
>
> Instead of waiting for STARTUP after INITs, BSP will execute
> the BIOS boot-strap code which is not a desired behavior for
> waking up BSP. To avoid the boot-strap code, wake up CPU0 by
> NMI instead.
>
> This works to wake up soft offlined CPU0 only. If CPU0 is hard offlined (i.e.
> physically hot removed and then hot added), NMI won't wake it up. We'll change
> this code in the future to wake up hard offlined CPU0 if real platform and
> request are available.
>
> AP is still waken up as before by INIT, INIT, STARTUP sequence.

Would clearing IA32_APIC_BASE_MSR.BSP avoid calling the BIOS code when
the cpu is brought back online?  Setting that flag in another cpu that
is still online might also allow suspend/resume to work.

--
Brian Gerst
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